Presently, twin-lead and tri-lead electric signal cables have an insulated conductor and at least one conductive drain wire. Around them is a shielding layer of helically-wrapped or longitudinally folded metal-coated polymer tape, metal foil tape, polymer tape filled with conductive materials, inherently conductive polymer tape, polymer tape having a conductive layer coated on each side which differ in composition, wire braid, or served wire. All this is jacketed with a single layer of jacket material, commonly of about 6 mil semiconductive insulation which may typically comprise, but is not limited to, conductive polyvinyl chloride (PVC) perfluoroalkoxy tetrafluoroethylene (PFA), copolymers of ethylene and tetrafluoroethylene (Tefzel), or polyvinylidene fluoride (Kynar) for example. Pinholes in the semiconductive jacketing occur in and are problems in these cables in that the pinholes are difficult to test for, owing to the semiconductive nature of the jacket material and are very difficult and expensive to correct when found. The present invention provides a unique and effective solution to these problems.